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FIG. 10. Illustrations of the nictitating membrane in the various animals named 

 drawn from nature. The letter N indicates the membrane in each case. In man 

 it is called the plica semilunarzs, and is represented in the two lower drawing! 

 under this name. In the case of the shark (Gaieus) the muscular mechaniun u 

 shown as dissected. 



